Studies of the molecular biology of the mycoplasmaviruses are to be continued. The effects of rifampicin and chloramphenicol on MVL51 replication and the nature of the viral modification of the cells' RNA polymerase will be examined. MVL2 host modification and restriction will be investigated to see whether it is due to a viral DNA or membrane change. Growth studies of MVL2 will be carried out. MVL51 ts mutants will be used to try to determine the number of viral genetic complementation groups. A mycoplasma cell mutant, which is phenotypically similar to Escherichia coli rep, will be studied. BIBLIOGRAPHIC REFERENCES: Das, J. and J. Maniloff (1975). Replication of mycoplasmavirus MVL51: 1. Replicative intermediates. Biochem. Biophys. Res. Commun. 66: 599-605. Maniloff, J. and A. Liss (1974). Comparative structure, chemistry, and evolution of mycoplasmaviruses. In "Viruses, Evolution and Cancer", (E. Kurstak and K. Maramorosch, eds.), pp. 583-604, Academic Press, Inc., New York.